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1 Hurunui River Dissolved Reactive Phosphorus Concentrations and Loads A tool to manage periphyton growth ? Review of Ecan & NIWA Dataset of DRP measurements.

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Presentation on theme: "1 Hurunui River Dissolved Reactive Phosphorus Concentrations and Loads A tool to manage periphyton growth ? Review of Ecan & NIWA Dataset of DRP measurements."— Presentation transcript:

1 1 Hurunui River Dissolved Reactive Phosphorus Concentrations and Loads A tool to manage periphyton growth ? Review of Ecan & NIWA Dataset of DRP measurements at SH1 Samples taken between 2004 to June 2014

2 Purpose of Presentation 2 What do the water quality samples in the Hurunui River tell us about Phosphorus Concentrations and Loads? How relevant is an in-river load limit to achieving in-river water quality outcomes? How should P Loads be measured relative to the baseline? Has the P Load Limit at SH1 really been exceeded? Should “landuse change” be a “permitted activity” or a “non-complying activity” under Rule 10.2(b) of the HWRRP?

3 Background: Periphyton Accumulation 3 NIWA study in April 2014; Study to determine if adding N and P to the Hurunui River results in additional growth of Periphyton; Results      Downstream of Balmoral forest: the growth of Periphyton is limited by the low concentration of Phosphorus in the river; the concentration of nitrates in the river can be increased without increasing the growth Periphyton.

4 DRP - Dissolved Reactive Phosphorus 4 12 Months of the Year Ignoring season and river flow … All year round DRP concentrations appear to be stable

5 DRP - Dissolved Reactive Phosphorus 5 Good news: DRP concentrations during the Summer months at flows less than 60 cumecs have declined. Summer Months at flows less then 60 cumecs

6 DRP (Concentration and Load) relationships with River Flow 6 There is a weak positive relationship between DRP Concentration and River Flow; There is a strong positive relationship between DRP Load and River Flow; High flow events that remove Periphyton also have high DRP loads;

7 More Good News: Hurunui River Flows since 2005 have been increasing 7 Average River Flows for the period are 14% higher than for the period But… Higher Flows = Higher DRP Loads

8 EXAMPLE Low flows = Low DRP Load 8 Low flows = limited flushing flows = lots of Periphyton accumulation = Low DRP Load  Change of land use remains a permitted activity !!!

9 9 High flows = flushing flows = Periphyton removal = DRP Load Limit exceeded  Change of land use becomes a non-complying activity !!! EXAMPLE – 2013 High flows = High DRP Load

10 DRP – Modelled* Annual Load and 6 year Rolling Average Load 10 Using the Ecan method to calculate Load, the 6 year average DRP load is increasing. This is because river flows are increasing; ____

11 BUT DRP Concentrations appear to be in decline !!! Has the Schedule 1 DRP load limit really been exceeded ??? To answer this question, we should apply the DRP concentrations to the river flows to determine if the Schedule 1 DRP load (regulating water quality) has been exceeded.

12 DRP – Average DRP Concentrations at River Flows between 20 to 90 cumecs 12 Taking River flow into account, DRP concentrations over the period are around 15% less than concentrations over the period ; After removing the impact river flows, we can conclude the DRP load is around 15% less than the equivalent DRP load; 25% less Statistically significant at 95% Confidence

13 DRP – Average DRP Concentrations : SUMMER River Flows (20 to 50 cumecs) 13 Summer DRP concentrations are much lower than the baseline

14 Load Limit - Conclusions 14 An in-river Load Limit is a very poor tool to manage in- river water quality and regulate landuse change; The HWRRP should replace “In-River Load Limits” with catchment wide: On-Farm N Load limits (t/ha/yr); & On-Farm Best Practice phosphorus management requirements. The DRP load is around 15% less than the equivalent average annual DRP load. Landuse change under Rule 10.2(b) should remain a permitted activity.

15 FARM GROUND WATER MAINSTEM SPRINGS/TRIBUTARY Invertebrate Toxicity & Periphyton effects Invertebrate Toxicity, Periphyton & toxic bloom effects Concentration Limits Nitrate-Nitrogen Toxicity Limits & Low-flow Phosphorus Limits Periphyton Objectives Concentration Limits Nitrate-Nitrogen Toxicity Limits & Low-flow Phosphorus Limits Periphyton Objectives HighMedium Low High Medium Low Limit: Effectiveness Farmer: Response and Incentive High Groundwater Quality Limit On-Farm Load Limit N-Loss (kg/ha/yr) & P-Loss Management Requirements; Replace in-river Load limits with: On-Farm (Catchment wide) N Load limit (t/ha/yr); & Best practice phosphorus management requirements. Water Quality Management - -Set Limits where they can be managed - -On-Farm Cause-Effect-Consequence-Reward Human Health & Consequential Lowland Stream, Tributary & Mainstem effects Medium Low

16 What is Ngai Tahu Property doing over the next 6 months A more comprehensive NIWA study this summer in the Hurunui River to measure the accumulation of Periphyton biomass over time, and in response to additional N & P; A Lincoln Agritech research project on groundwater flows and in-river N & P concentrations impacting the Hurunui River; Preparation of a “Best Practice Phosphorus Manual” specific to the Hurunui Catchment; Based on the above information (April/May 2015), consider the implications for N & P management and the need for a Plan Change.


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